Hair color is determined by the relative amounts of the brown-black pigment eumelanin and the red-yellow pigment pheomelanin in follicular melanocytes. Increasing melanogenesis leads to increasing the melanin content of melanocytes, and hence results in increased pigmentation or darkened color of the skin, hair wool or fur.
U.S. Pat. No. 5,352,440 is directed to increasing melanin synthesis in melanocytes and increasing pigmentation by administration of certain diacylglycerol compounds. U.S. Pat. No. 5,532,001 is directed to increasing pigmentation in mammalian skin via administration of certain DNA fragments. U.S. Pat. No. 5,554,359 is directed to increasing levels of melanin in melanocytes by administration of lysosomotropic agents.